1. Field of the Invention
The present invention relates to a numerical controller and, more particularly, relates to a numerical controller which includes a taper angle compensating function of taper machining in skiving.
2. Description of the Related Art
Skiving refers to a machining method for cutting a workpiece by feeding a cutting tool in a tangential direction of the workpiece when cutting the workpiece by using the turning machine (JIS Standard B0106 0.209). Skiving is performed, in a turning machine, by using a tool having a linear blade disposed diagonally with respect to an axis of rotation of a workpiece on a YZ plane and moving the tool on a Z axis and a Y axis (see, for example, JP 2003-516868 A (corresponding to WO01/043902)).
In a skiving work using a turning machine, machining of a tapered shape can be carried out in taper machining by moving an X-axis following the moving of a Z-axis and a Y-axis, making a diagonal movement instruction, as illustrated in FIGS. 7A and 7B.
However, in skiving work in a turning machine, a position (cutting point 5) at which a linear blade 41 contacts a workpiece 3 changes from a point of cutting start time to a point of cutting end time. Therefore, as illustrated in FIG. 8, a movement amount of the Z axis in a cutting path is larger than a movement amount of the tool 4 on the Z axis instructed by a program instruction (note that a scale of FIG. 8 is enlarged in an X axis direction in order to make these figures clearly understandable). Therefore, there is a problem that, if the movement amount of the X axis based on a program instruction is simply determined on the basis of the movement amount of the Z axis based on the program instruction, a taper angle θr in an actual cutting path does not match with a taper angle θcmd which is determined by the movement amount of the X axis and the movement amount of the Y axis based on the program instruction.
Further, as illustrated in FIGS. 9A and 9B, when the tool 4 is inclined due to an attachment error or the like, a position of the cutting point 5 on an X axis coordinate changes from the point of cutting start time to the point of cutting end time. Hence, there is a problem that a taper angle after machining changes due to change in a position of the cutting point 5 on the X axis coordinate from the point of cutting start time and the point of cutting end time, in addition to change in a taper angle based on a difference between the movement amount of the Z axis based on the program instruction and the movement amount of the Z axis in a cutting path.